Hillock formation on high-temperature annealed AlN templates due to dislocation nucleation at AlON particles

Abstract

The origin of hillocks in AlGaN layers grown on high-temperature annealed (HTA) AlN templates has been reinvestigated. During the HTA process, AlON precipitates form within the AlN matrix due to oxygen contamination. The thermal mismatch between the precipitates and the compressively strained AlN generates shear stress on pyramidal glide planes, which provide the glide system for (a + c) dislocations. Importantly, the proximity of a precipitate to the free surface amplifies this localized shear field and lowers the barrier for half-loop formation, making subsurface precipitates the most effective dislocation sources. Once the shear stress reaches a critical value, a single (a + c) dislocation half-loop nucleates. The threading segments of the loop terminate at the HTA-AlN surface and trigger spiral growth during AlGaN epitaxy, ultimately leading to hillock formation.